Over the years anglers have learned that fish sometimes strike at bait and run with it before swallowing it. If a fish feels the immediate tension of the fishing line, often the fish will drop it. Therefore, anglers leave slack in the line so the fish has running room after a strike. This is done by leaving the bail open or drawing out enough line and closing the bail. Neither of these methods are particularly effective while trolling, in rough weather or when live bait is used. Sometimes anglers will place their rods on the ground or in a rod holder and place small rocks on their lines to keep excess slack from running out of reel but allowing the fish to pull the line from under the rocks and run with it. This method is extremely imprecise and is often foiled by movement of the boat or rod. Furthermore, it is difficult to see when a fish strikes and near impossible to see in the dark.
A great deal of the art of fishing is knowing when to "set the hook" after a fish strikes. It is important to know exactly when a fish strikes and to allow the fish enough time and room to run with the bait. Various devices have been provided to be used in association with fishing rods and lines to signal that a fish has struck. U.S. Pat. No. 4,541,195 teaches a line tension indicator that does not release the line at a strike but gives a signal when it senses increased tension. U.S. Pat. No. 4,142,316 teaches a fishing rod holder that includes a pressure sensitive device which generates a signal during an excessive downward pull on the line. U.S. Pat. No. 3,992,797 teaches a line tension indicator that does not release the line at a strike but gives a signal when it senses increased tension. U.S. Pat. No. 3,868,668 a line tension indicator that does not release the line at a strike but gives a signal when it senses increased tension but also generates a constant signal if a single large amount of tension is applied to the line. U.S. Pat. No. 3,624,689 teaches a line guide at the tip of a fishing rod that senses and indicates sharp contrasts in line movement or tension. In each of the foregoing patent publications the strike indicators sense increased tension in the line. Each indicator requires that the bail be closed to work properly, otherwise no change in tension will occur because more line will just be released from the reel. Furthermore, most are designed such that the line must at all times pass through some component and remain there during the entire landing procedure.
Some devices have combined means for gripping the line until a fish strikes and means for providing a signal upon the release of the line. U.S. Pat. No. 4,586,284 teaches a line indicator device where the line is held between two friction plates such that the removal of the line allows the spring to close contacts creating a signal. U.S. Pat. No. 3,959,910 teaches a line indicator device that grips the line and generates a signal as the line is removed from the grip arms.
All the strike indicators shown in the patent publications listed above are electronic devices and are subject to the problems common to all electrical devices around water. Furthermore, the additional weight of batteries may change the fundamental feel and balance of a rod such that the devices would need to be removed for more comfortable casting.